1 /* 2 * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com> 3 * 4 * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time. 5 * 6 * This program is particularly useful to measure the latency of nthread wakeups 7 * in non-error situations: all waiters are queued and all wake calls wakeup 8 * one or more tasks, and thus the waitqueue is never empty. 9 */ 10 11 /* For the CLR_() macros */ 12 #include <pthread.h> 13 14 #include <signal.h> 15 #include "../util/stat.h" 16 #include <subcmd/parse-options.h> 17 #include <linux/compiler.h> 18 #include <linux/kernel.h> 19 #include <linux/time64.h> 20 #include <errno.h> 21 #include "bench.h" 22 #include "futex.h" 23 24 #include <err.h> 25 #include <stdlib.h> 26 #include <sys/time.h> 27 28 /* all threads will block on the same futex */ 29 static u_int32_t futex1 = 0; 30 31 /* 32 * How many wakeups to do at a time. 33 * Default to 1 in order to make the kernel work more. 34 */ 35 static unsigned int nwakes = 1; 36 37 pthread_t *worker; 38 static bool done = false, silent = false, fshared = false; 39 static pthread_mutex_t thread_lock; 40 static pthread_cond_t thread_parent, thread_worker; 41 static struct stats waketime_stats, wakeup_stats; 42 static unsigned int ncpus, threads_starting, nthreads = 0; 43 static int futex_flag = 0; 44 45 static const struct option options[] = { 46 OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"), 47 OPT_UINTEGER('w', "nwakes", &nwakes, "Specify amount of threads to wake at once"), 48 OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"), 49 OPT_BOOLEAN( 'S', "shared", &fshared, "Use shared futexes instead of private ones"), 50 OPT_END() 51 }; 52 53 static const char * const bench_futex_wake_usage[] = { 54 "perf bench futex wake <options>", 55 NULL 56 }; 57 58 static void *workerfn(void *arg __maybe_unused) 59 { 60 pthread_mutex_lock(&thread_lock); 61 threads_starting--; 62 if (!threads_starting) 63 pthread_cond_signal(&thread_parent); 64 pthread_cond_wait(&thread_worker, &thread_lock); 65 pthread_mutex_unlock(&thread_lock); 66 67 while (1) { 68 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR) 69 break; 70 } 71 72 pthread_exit(NULL); 73 return NULL; 74 } 75 76 static void print_summary(void) 77 { 78 double waketime_avg = avg_stats(&waketime_stats); 79 double waketime_stddev = stddev_stats(&waketime_stats); 80 unsigned int wakeup_avg = avg_stats(&wakeup_stats); 81 82 printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n", 83 wakeup_avg, 84 nthreads, 85 waketime_avg / USEC_PER_MSEC, 86 rel_stddev_stats(waketime_stddev, waketime_avg)); 87 } 88 89 static void block_threads(pthread_t *w, 90 pthread_attr_t thread_attr) 91 { 92 cpu_set_t cpu; 93 unsigned int i; 94 95 threads_starting = nthreads; 96 97 /* create and block all threads */ 98 for (i = 0; i < nthreads; i++) { 99 CPU_ZERO(&cpu); 100 CPU_SET(i % ncpus, &cpu); 101 102 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu)) 103 err(EXIT_FAILURE, "pthread_attr_setaffinity_np"); 104 105 if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) 106 err(EXIT_FAILURE, "pthread_create"); 107 } 108 } 109 110 static void toggle_done(int sig __maybe_unused, 111 siginfo_t *info __maybe_unused, 112 void *uc __maybe_unused) 113 { 114 done = true; 115 } 116 117 int bench_futex_wake(int argc, const char **argv, 118 const char *prefix __maybe_unused) 119 { 120 int ret = 0; 121 unsigned int i, j; 122 struct sigaction act; 123 pthread_attr_t thread_attr; 124 125 argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0); 126 if (argc) { 127 usage_with_options(bench_futex_wake_usage, options); 128 exit(EXIT_FAILURE); 129 } 130 131 ncpus = sysconf(_SC_NPROCESSORS_ONLN); 132 133 sigfillset(&act.sa_mask); 134 act.sa_sigaction = toggle_done; 135 sigaction(SIGINT, &act, NULL); 136 137 if (!nthreads) 138 nthreads = ncpus; 139 140 worker = calloc(nthreads, sizeof(*worker)); 141 if (!worker) 142 err(EXIT_FAILURE, "calloc"); 143 144 if (!fshared) 145 futex_flag = FUTEX_PRIVATE_FLAG; 146 147 printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), " 148 "waking up %d at a time.\n\n", 149 getpid(), nthreads, fshared ? "shared":"private", &futex1, nwakes); 150 151 init_stats(&wakeup_stats); 152 init_stats(&waketime_stats); 153 pthread_attr_init(&thread_attr); 154 pthread_mutex_init(&thread_lock, NULL); 155 pthread_cond_init(&thread_parent, NULL); 156 pthread_cond_init(&thread_worker, NULL); 157 158 for (j = 0; j < bench_repeat && !done; j++) { 159 unsigned int nwoken = 0; 160 struct timeval start, end, runtime; 161 162 /* create, launch & block all threads */ 163 block_threads(worker, thread_attr); 164 165 /* make sure all threads are already blocked */ 166 pthread_mutex_lock(&thread_lock); 167 while (threads_starting) 168 pthread_cond_wait(&thread_parent, &thread_lock); 169 pthread_cond_broadcast(&thread_worker); 170 pthread_mutex_unlock(&thread_lock); 171 172 usleep(100000); 173 174 /* Ok, all threads are patiently blocked, start waking folks up */ 175 gettimeofday(&start, NULL); 176 while (nwoken != nthreads) 177 nwoken += futex_wake(&futex1, nwakes, futex_flag); 178 gettimeofday(&end, NULL); 179 timersub(&end, &start, &runtime); 180 181 update_stats(&wakeup_stats, nwoken); 182 update_stats(&waketime_stats, runtime.tv_usec); 183 184 if (!silent) { 185 printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n", 186 j + 1, nwoken, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC); 187 } 188 189 for (i = 0; i < nthreads; i++) { 190 ret = pthread_join(worker[i], NULL); 191 if (ret) 192 err(EXIT_FAILURE, "pthread_join"); 193 } 194 195 } 196 197 /* cleanup & report results */ 198 pthread_cond_destroy(&thread_parent); 199 pthread_cond_destroy(&thread_worker); 200 pthread_mutex_destroy(&thread_lock); 201 pthread_attr_destroy(&thread_attr); 202 203 print_summary(); 204 205 free(worker); 206 return ret; 207 } 208